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Zapping Corrosion

Finishing Today Magazine
by Col. Ron Savin
May 9, 2008

PROBLEM: Conventional zinc-rich coatings based on zinc dust have been limited to maintenance primer applications that require a blasted substrate for effective performance.

SOLUTION: Advanced coatings containing a low-cost, highly conductive zinc flake material can galvanize heavy rust, thereby eliminating the need for costly sandblasting and a conventional coat of zinc-rich primer. Anti-Corrosion CoatingThe coatings also can be used to prevent fouling in marine applications.

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Hyperzinc - Technology Update Print

ZINC FLAKE and ZINC-RICH TECHNOLOGY
Recent Improvements
By Ronald R. Savin (Colonel, USAF ret)

The development of inorganic zinc rich primers over half a century ago has provided the coatings industry with its most effective technology to resist corrosion for the protection of locks, dams, bridges, off shore oil platforms, ships and port facilities etc..

Problems associated with the manufacture, storage, handling, cost and application of these primers both inorganic and organic have limited their utilization to approximately 10 million gallons annually on a worldwide basis. These "deficiencies" to a large extent have narrowed this technology to the area of air dry maintenance primers requiring a blasted substrate for effective performance.

The current market for non zinc-rich primers designed to resist corrosion is infinitely larger than the current contribution of zinc rich technology. The purpose of my development program during the past few years was to improve zinc rich technology by reducing design constraints, including cost, density, ease of manufacture while improving overall cathodic performance to promote superior anti-corrosion properties for both air dry and baking applications.


ZINC FLAKE

The high cost of zinc flake produced by the wet milling process has caused the paint industry to treat this very effective zinc pigment as somewhat of a laboratory curiosity. Its current commercial application largely involves the plating of fasteners where it effectively competes with zinc electroplating concerning price and quality objectives. Hyperseal has recently succeeded in developing a process of dry milling zinc flake that is equal or superior in quality to the wet milling process at a fraction of the cost of wet milling!

Zinc flake has been recognized as a superior corrosion resistant pigment by both the coatings and fastener industry. It is conventionally manufactured by ball milling, using a lubricant such as stearic acid and mineral spirits, to produce a lamellar particulate with impressive leafing properties.

The flaking of zinc dust and zinc powder by wet milling in a solvent flattens the zinc particulate into a lamellar structure by modifying the aspect ratio and considerably reducing the apparent density of the zinc powder. In other words the actual area of coverage of the zinc particulate has been virtually tripled during the milling process. This wet milling process is extremely expensive, consequently the paint industry has continued to use zinc dust in their formulations rather than the very effective flake.

Zinc flake produced by the Hyperseal process is equal or superior to the conventional wet milling process at a fraction of processing cost.

Laboratory results have consistently demonstrated that the proper incorporation of zinc flake in both organic and inorganic primers reduces the optimum zinc to binder ratio as much as three quarters while improving physical and application properties.

Currently the utilization of zinc-rich waterborne primers for industrial application is rather limited due to marginal adhesion and insufficient flexibility to meet rigid industrial specifications.

I have also modified the waterborne silicate binders to incorporate zinc flake into zinc rich primers that are cathodically effective in both conventional air dry maintenance and baking moving line industrial applications. These modified binders incorporating zinc flake have been designed to meet most specifications for industrial application at competitive material cost while dramatically reducing density and pigment volume concentration providing remarkable ease of application.

I have recently been able to improve zinc flake quality to incorporate a large percentile of zinc flake into epoxy binders to produce a cathodic zinc flake epoxy superior to most zinc rich epoxy primers for both solvent borne and electrostatic powder application.

This development is of considerable importance as conventional powder extrusion equipment has not proven effective for the inclusion of sufficient zinc or zinc flake to produce a zinc rich electrostatic powder with an adequate zinc to binder ratio for effective corrosion resistance.

This development will permit the powder coatings industry to provide an effective zinc rich primer to produce powder coatings with impressive corrosion resistance and should be of considerable interest to improve the corrosion resistance of products exposed to extreme environmental conditions such as reinforcement bars, construction, transportation equipment etc...

Recent development has demonstrated that properly formulated Zinc Flake Primers both organic and inorganic with rust (thin and deep rust) virtually passivating or in essence galvanizing rust from further oxidation. This phenomenon permits rusted areas on ships, bridges, guardrails etc. to be primed without blasting to be top coated with a durable coating.


This development offers industry a cost effective method of protecting rusted surfaces from further deterioration.

Panels of light and heavy rusted panels were coated with the zinc flake primer and exposed to B - 117 salt fog from several days to several months with virtually little to no rust creepage into the zinc flake primer.

In order to determine the efficiency of priming over rust, a series of rusted panels (light and heavy rust) were coated with three primers containing 1. stainless steel flake, 2. nickel and 3. aluminum flake at a ratio of six parts of flake to epoxy binder.

These primers: 

  1. stainless steel flake,
  2. nickel flake and
  3. aluminum flake

were exposed to B-117 salt fog for one week. The results of these tests were extremely conclusive. All of the panels primed with stainless steel, nickel and aluminum flake were totally rusted through within 100 hours, showing little to no primer visible. The zinc flake primer over rust demonstrated better performance than the control panels that had been blasted to white rust indicating that the reaction of zinc flake with rust may be producing a composite alloy more corrosion resistant than conventional zinc dust primers.

The potential savings for the maintenance of steel structures by reducing sandblasting and coating rust with a Zinc Flake Primer would significantly lower the considerable cost of the maintenance once this development has been accepted as effective.

Another potential application of zinc flake development is in the area of anti-fouling conventionally protected with a coating containing a high level of cuprous oxide and rosin permitting the ablation of the oxide with a slow release of the copper biocide. This release is basically total, requiring periodic recoating as virtually all of the cuprous oxide has been ablated into the surrounding salt water.

I exposed several dozen panels coated with zinc flake primer in San Diego Bay and the warm waters of Fort Lauderdale. After a period of eight months the results of the initial tests were rather impressive. The panels coated with the zinc flake primer were relatively pristine with very little fouling. This control was USN Navy specification MIL-P-15169 containing approximately 14 pounds per gallon of cuprous oxide and 50% rosin in the vinyl chloride binder to permit a slow release of the biocide.

After several months exposure the Navy control panels in San Diego were free of barnacles, however, these panels were covered with slime. The zinc flake panels were virtually pristine with no fouling.

The zinc flake panels submerged in South Florida exhibited a few barnacles and worms. The Navy panel (MIL-P-15169) was covered with barnacles. These tests are not conclusive; further tests are in order to evaluate the use of a zinc flake non ablative primer on ship bottoms to determine eff i c a c y. The extreme reactivity of the zinc flake when exposed to salt water produces white rust, (zinc carbonate and zinc oxide) which is resistant to barnacle formation.

These tests are to be evaluated on an empirical basis on ship bottoms; however,

the positive effect of zinc flake over rust has been tested repeatedly without further rusting of the primer in excess of 1000 hours of salt fog exposure without top coating.

U.S. Patent #6,638,628 B2 was developed as a duplex coating with or without zinc flake to replace carcinogenic chromic acid conventionally applied to most galvanize to retard rapid deterioration by white rust. Federal Law outlawed the application of chromic acid over galvanize in 2006.

The superior quality of LOW COST CATHODIC PROTECTION provided by zinc flake is currently available to protect most manufactured products with waterborne, solvent and electrostatic zinc flake powder.